Geosciences

The reading of Earth history satisfies a fundamental human urge to know how the world around us came to be. Throughout its 4.6 billion year history the Earth has undergone enormous transformation and stable isotope analysis has been at the forefront of developing our knowledge of these transformative processes. By understanding the macro and micro cycling mechanisms of the light stable isotopes through the lithosphere by natural processes the Earth history is continually being understood in ever more detail.

Paleoclimate

One of the earliest applications of light stable isotope mass spectrometry was the reconstruction of ancient climate based on the oxygen isotopic composition (δ18O) of preserved ancient marine carbonate, and continues to be one of the widely utilised methods for interrogating Earth’s climate history. This paleothermometer is based on the fundamental principle that the fractionation of oxygen isotopes into calcite is temperature dependent. The isoprime precisION with Dual Inlet and MultiCarb enables very precise and reliable automated measurement of carbonates, ideal for generating high-resolution paleo temperature records.

Cosmology

The sulfur isotope analysis of extra-terrestrial sulphide minerals, e.g. from meteorites, has provided a variety of insights into the origins of the Earth and the solar system. The isotopic composition of meteoritic sulfur (Canyon Diabolo triolite) was also used as a the original reference point for the bulk earth from which to evaluate global scale fractionations in the sulfur cycle. Sulfur-bearing minerals are easily analysed with our range of elemental analyser (EA-IRMS) systems, which utilise advanced purge and trap (APT) technology for unbeatable separation and peak focussing of SO2, ensuring perfect resolution and unparalleled sensitivity for mineral sulfur analysis.

Stratigraphy

Fluctuations in δ13C through geological time are brought about by changes in the balance of fluxes of the carbon cycle. Because the residence time in the carbon cycle is brief (10 ka), changes in flux are recorded accurately and globally in the sedimentary record. As such, occasional spikes in the global δ13C are useful as stratigraphic markers for chemostratigraphy, especially during the Paleozoic. The iso FLOW uses our novel UltiTrap technology to enable precise, high throughput continuous flow analysis of bulk carbonates to identify these isotope excursions.

Geoscientific publications using our instruments

Our customers use our instruments to do some amazing research in the geosciences. To show you how they perform their research and how they use our IRMS instruments, we have collected a range of peer-reviewed publications which cite our products. You can find the citations below and then follow the links to the publishing journal should you wish to download the publication.

If you would like to investigate our available citations in more detail, or email the citation list to yourself or your colleagues then take a look at our full citation database.

Flake graphite mineralisation is hosted in the Kuummiut Terrane of the Paleoproterozoic Nagssugtoqidian Orogen, south-east Greenland. Eclogite-facies peak-metamorphic assemblages record temperatures of 640–830 °C and pressures of 22–25 kbar, and are retrogressed in the high-pressure amphibolite-facies during ca. 1870–1820 Ma. Graphite occurs as lenses along cleavage planes in breccia and as garnet-quartz-graphite veins in various metamorphic host rocks in the Tasiilaq area at Auppaluttoq, Kangikajik, and Nuuk-Ilinnera. Graphite contents reach >30 vol% in 0.2–4 × 20 m wide semi-massive mineralisation (Auppaluttoq, Kangikajik). Supergene alteration formed 1- to 2-m-thick and up to a 2.5 × 2.5 km wide loose limonitic gravel containing graphite flakes in places. The flake size ranges from 1 to 6 mm in diameter with an average of ~3 mm. Liberation efficiency is at minimum 60%. Hydrothermal fluids at ~600 °C, transporting carbon as CO2 and CH4, formed the mineralisation commonly hosted by shear zones, which acted as pathways for the mineralising fluids. The hydrothermal alteration assemblage is quartz-biotite-grunerite-edenite-pargasite-K-feldspar-titanite. The δ13C values of graphite, varying from −30 to −18‰ PDB, indicate that the carbon was derived from organic matter most likely from metasedimentary sources. Devolatilisation of marble may have contributed a minor amount of carbon by fluid mixing. Precipitation of graphite involved retrograde hydration reactions, depleting the fluid in H2O and causing graphite saturation. Although the high-grade mineralisation is small, it represents an excellent example of hydrothermal mineralisation in an eclogite-facies terrane during retrograde exhumation.

Mengxiong Wu, Xingguo Han, Ting Zhong, Mengdong Yuan, Weixiang Wu

Recalcitrant biochar application appears to be a promising method to decelerate global warming through increasing long-term carbon sequestration in soil. Stability of biochar carbon (C), which is the major determining factor of C sequestration effect, depends mainly on biochar physiochemical characteristics and soil properties. However, little is known about biochar C stability in paddy soil. In this study, 13C labeled rice straw (RS) biochar produced at 500°C was incubated with five types of paddy soils to determine the key soil characteristics involved in biochar-C stability. Results showed that cumulative mineralization rates of RS biochar-C incubated with different paddy soils were relatively low (0.17–0.28%) during 390days of incubation. The cumulative mineralization rates of RS biochar-C increased with the increasing native soil total organic carbon (TOC) content. The estimated mean residence time (MRT) of stable C components of RS biochar in paddy soil, varying from 617 to 2829 years, decreased with the increase of soil TOC content. In addition, greater atomic O/C ratio and oxygen-containing functional groups were observed in biochar samples incubated in paddy soils with higher TOC content. These results suggest that RS biochar application could be an effective method for C sequestration in paddy soil. However, the stability of RS biochar in paddy soil would be significantly impacted by soil TOC content. From the perspective of long-term C sequestration, RS biochar is more suitable for applying in paddy soils with lower TOC content.

Yan Li, Zhiguang Song, Xin-xing Cao, Simon C. George

The abundance and composition of organic matter and the δ13C compositions of some specific individual compounds were analysed in sediments collected from an excavated profile of the Early Cretaceous Yi-xian Formation in Liaoning Province, NE China, in order to provide organic geochemical information on palaeoclimate and environmental changes. The distribution of n-alkanes varies steadily through the profile, with long-chain n-alkanes dominating in the lower and upper sections, and medium chain-length n-alkanes dominating in the middle section of the profile. The δ13C values of n-alkanes, hopanes and steranes show similar upward positive trends through the profile, suggesting that these compounds originated from the same source material and also reflect consistent changes in the environment of the sedimentary basin. The C24 17,21-secohopane was only detected in the lower and middle sections of the profile and has a more positive carbon isotopic composition by about 3.7–6.7‰ than that of associated n-alkanes, hopanes, steranes and C30 8,14-secohopane. This implies that the C24 17,21-secohopane had a different origin, possibly connected with the volcanic ash deposits and massive vertebrate remains. Reconstruction of the δ13C composition of atmospheric CO2 based on plant-derived C29 and C31 n-alkanes shows a change from –10‰ to –3‰ from the bottom to the middle of the profile. This upward positive excursion through the profile is consistent with the worldwide variation of atmospheric CO2 during the Early Cretaceous and indicates an upward warming trend, likely related to globally intensified volcanic activity.

The Late Cretaceous is often characterized as having a variable greenhouse climate, however, the relatively few continental sites preserving geologic records from this time exist limiting information on terrestrial climate and environments. Worldwide, the Songliao Basin (SLB) of northeastern China is one of the largest Cretaceous-age continental rift basins. Thus, this well-preserved lacustrine deposit provides a unique record of terrestrial paleoenvironmental conditions during the Cretaceous. Here, we report organic geochemical data from Late Cretaceous-age lacustrine deposits (lower Nenjiang Formation) from the eastern side of the SLB. Outcrop samples were collected from the Houjingou section and the following analyses performed: (1) total organic carbon (TOC) content and isotopic composition, (2) biomarker distribution, including the identification and determination of relative amounts of both aliphatic and aromatic hydrocarbons and steranes, and (3) compound specific stable carbon and hydrogen isotopic compositions of n-alkanes. The biomarker distribution and stable carbon isotopic values (δ13C) of the TOC indicate organic matter (OM) from the uppermost section of the first member of the Nenjiang Formation (Upper K2n1) was mainly sourced from aquatic macrophytes and land plants. In the lower part of the second member of the Nenjiang Formation (Lower K2n2) the biomarker distribution and δ13C of both the TOC and n-alkanes indicate that OM was sourced from a mixture of algae, bacteria, and higher plants. As a result of marine transgression, seawater incursions, indicated by the presence of 24-n-propyl-cholestanes and 24-iso-propyl-cholestanes, occurred episodically in Lower K2n2. The negative hydrogen isotopic composition (δ2H) of short chain n-alkanes in Lower K2n2 indicate an extremely humid environment and it is likely that an influx of freshwater caused large-scale flooding of the Songliao Paleo-lake. High-resolution biomarker and stable isotope records from the Houjingou section demonstrate abrupt environmental changes in the Songliao Paleo-lake following seawater incursions during the Late Cretaceous.

The Late Cryogenian Warm Interval (LCWI) refers to a non-glacial interval that separates presumed representatives of the Sturtian and Marinoan panglaciations. Its duration is poorly constrained radiometrically and its deposits are relatively poorly known in most geographic regions. This paper aims to constrain the duration, palaeoenvironments and petrogenesis of such deposits in the classic region of NE Spitsbergen, Svalbard. The succession comprises a 200-205 m dolomitic shale (Macdonaldryggen Member, known as E3, of the Elbobreen Formation) overlain by oolitic dolomite Slangen Member (E4), 15-25 m thick, with limestone developed at top and base of E3 in the south of the area. The assumed age context of the succession has been confirmed by the presence of a typical Sturtian cap carbonate profile of negative to positive δ13C, and primary Sr isotope compositions of basal E3 limestones <0.7072 and of upper E3 limestones of 0.7076. At the base of E3, interstratification of cap carbonate with ice-rafted and redeposited glacial sediments occurs. Early diagenetic stabilization of carbonate mineralogy from a precursor, possibly ikaite, to calcite or dolomite is inferred. E3 is predominantly dolomitic silt-shale, with sub-millimetre lamination, lacking sand or current-related sedimentary structures. Thin fine laminae are partly pyritized and interpreted as microbial mats. Dolomite content is 25-50%, with δ13C values consistently around +4‰, a value attributed to buffering by dissolution of a precursor metastable carbonate phase. Local calcite cement associates with low δ13C values. The carbonates form silt-sized, chemically zoned rhombic crystals from an environment with dynamically changing Fe and Mn. Three-dimensional reconstructions of cm-scale disturbance structures indicate that they represent horizontally directed sock-like folds, developed by release of overpressure into thin surficial sediment overlying an early-cemented layer. A shoaling upwards unit near the top of E3 displays calcium sulphate pseudomorphs in dolomite in the north, but storm-dominated limestones in the south, both being overlain by peritidal oolitic dolomites, exposed under the succeeding Wilsonbreen glacial deposits. There is no Trezona δ13C anomaly, possibly implying top-truncation of the succession. Regular 0.5 m-scale sedimentary rhythms, reflecting subtle variations in sediment texture or composition occur throughout E3 and are interpreted as allocyclic. They are thought to be mainly primary in origin, locally modified slightly during early diagenetic cementation. Rhythms are proposed to represent ca. 18 kyr precession cycles, implying 6-8 Myr deposition between glaciations.

Formation and evolution of solid bitumen during oil crackingMarine and Petroleum Geology (2016)

Solid bitumen is widespread throughout lower Paleozoic paleo-reservoirs in southern China. However, the processes that control its formation and evolution remain unclear. Here, we document temporal changes in the yield and characteristics of solid bitumen generated during oil cracking using an experimental approach involving the anhydrous pyrolysis of crude oil. The results indicate that solid bitumen is predominantly produced in environments of high thermal maturity associated with the dry gas stage of oil cracking (i.e., during rapid methane generation and C2–C5 gaseous hydrocarbon destruction), with maximum solid bitumen yields up to about 42% of the original amount of crude oil. A near linear relationship exists between solid bitumen yields and methane abundance during the main stage of solid bitumen formation, although there is no clear variation in the δ13C values of solid bitumen produced at any stage of this process. This suggests that the isotopic composition and distribution of solid bitumen within a reservoir can be used to identify hydrocarbon sources, delineate the range of paleo-reservoirs, and assess the size of paleo-oil reservoirs and oil-cracked gas reservoirs within a basin.

The Nanhuan manganese deposits in the southeastern Yangtze Platform occur in the black shale series in the lower part of the Datangpo Formation. In order to constrain the genesis of the deposits, a detailed study was undertaken that involved field observations, major and trace element analyses, organic carbon analyses, and isotope analyses (C, O, S). The major findings are as follows. (1) The ore-bearing rock series, morphology of the ore bodies, and characteristics of ores in several deposits are similar. The ore minerals are rhodochrosite and manganocalcite. The gangue minerals are mainly quartz, feldspar, dolomite, and illite. Minor apatite and bastnaesite occur in the manganese ores. (2) The ores are enriched in Ca and Mg, whereas they are depleted in Si, Al, K, and Ti compared to wall rocks. The ores normalized to average Post-Archean Australian shale (PAAS) are enriched in Co, Mo, and Sr. The chondrite-normalized rare earth element (REE) patterns for ores and wall rocks are between those of typical hydrogenous and hydrothermal type manganese deposits. Additionally, the ores have positive Ce anomalies with an average Ce/Ce* of 1.23 and positive Eu anomalies with an average Eu/Eu* of 1.18 (normalized to PAAS). (3) The average content of organic carbon is 2.21% in the samples, and the average organic carbon isotopic value (δ13CV-PDB) is −33.44‰. The average inorganic carbon isotopic value (δ13CV-PDB) of carbonates in Gucheng is −3.07‰, while the values are similar in the other deposits with an average of −8.36‰. The oxygen isotopic compositions (δ18OV-PDB) are similar in different deposits with an average of −7.72‰. (4) The sulfur isotopic values (δ34SV-CDT) of pyrite are very high and range from +37.9‰ to +62.6‰ (average of 52.7‰), which suggests that the pyrite was formed in restricted basins where sulfate replenishment was limited. The sulfate concentrations in the restricted basins were extremely low and enriched in δ34S, which resulted in the very high δ34S values for the pyrite that formed in the manganese deposits. Therefore, a terrigenous weathering origin for manganese can be excluded; otherwise, the sulfate would have been introduced into the basins together with terrigenous manganese, which would have decreased the δ34S values of pyrites. The manganese, which originated from hydrothermal processes, was enriched in the restricted and anoxic basins, and then, it was oxidized to manganese oxyhydroxide in the overlying oxic waters whereby the products precipitated into the sediments. The manganese oxyhydroxide in the sediment was then reduced to Mn2+ and released to the pore waters during the process of diagenesis. Some organic carbon was oxidized to CO32−, which made the depletion of 13C in manganese carbonates. Therefore, we suggest that the Nanhuan manganese deposits are hydrothermal–sedimentary/diagenetic type deposits.

We examined the role of reactive iron (FeR) in preserving organic carbon (OC) across a subaerial chronosequence of the Wax Lake Delta, a prograding delta within the Mississippi River Delta complex. We found that ~15.0% of the OC was bound to FeR, and the dominant binding mechanisms varied from adsorption in the youngest subaerial region to coprecipitation at the older, vegetated sites. The δ13C of the iron-associated OC was more negative than the total OC (mean = −2.6‰), indicating greater preference for terrestrial material and/or compounds with more negative δ13C values. However, only the adsorbed OC displayed preferential binding of lignin phenols. We estimate that ~8% of the OC initially deposited in deltaic systems is bound to FeR (equivalent to 6 × 1012 gC yr−1), and this percentage increases postdepositionally, as coprecipitation of FeR and OC allows for an even greater amount of OC to be bound to FeR.

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